Wireless transmitter



Aug. 18, 1931. N, E D s ETAL 1,819,596

WIRELES S TRANSMI TTER Criginal Filed Oct, 9, 1925 A M n okczzz- 0,201

INVENTOR N E. DAVIS W- -I- DITC AM 7 BY I (1 a W TORNEY Patented Aug. 18, 1931 UITED STATES feATE T OFFICE i NORMAN EUsTAonnAvIs'oF cnntmsnonn, AND. WILLIAM ,rnnononn :oIrcnAM, or COLCI-IESTER, ENGLAND, Asses-None To nani'o CORPORATION or AMERICA, A

CORPORATION OF DELAWARE WIRELESS TRANSMITTER February The present invention relates toan improved method and means for signaling by means of vacuum tube transmitters, and is particularly applicable to such transmitters when large. power is employed and when it is required to transmit signals at high speed.

It is afurther object of the invention to provide a method of controlling the amplitude of oscillations of transmitters of high power.

t is a further object of thisinvention to provide an adjustable means for controlling the amplitude of employed oscillations in a transmitting circuit in which high voltages are used in the transmitting device.

Other objects of the invention will appear from the following description of the'invent-i on taken in connection with the accompanying drawings in which Fig. 1 is a diagrammatic view of the circuits and triodes arranged according to the preferred form of the present invention; and,

Fig. 2 shows a modification of the inventi-on shown inliig. 1. Like letters and like characters are used throughout the specification and drawings to describe like parts of the circuits and apparatus.

Vacuum tube transmitters of high power are usually operated according to the socalled independent drive principle, that is, the main oscillatory power is. generated by means of ai number of vacuum tubes or tri odes, the grids of which are excited from a lowpower vacuum tube (generally termed the independent drive).

It is also a well knownpractice-to.interpose an intermediate bankoi vacuum tubes between the independent drivecir'cuit and themain oscillator and to supply the anode voltage to both these banks of vacuum tubes from a common source of electrical power of high voltage.

Occasionally also the independent drive is supplied from the same source of power, but more commonly it is supplied from aseparate source.

According to our present invention a resistance is inserted in the lead from the high voltage generator to the intermediate and in Great Britain October 13, 1924. Renewed 18, 1931.

amplifier vacuum tube anodes in such a position that the anode current of the intermediate amplifier or vacuum tube passes through this resistance but the anode current. of the main amplifier does not. In ad'- dition, a vacuum tube or a number of vacuum tubes,hereinafter called the absorber, is connected in such a manner as to be in series with the resistance and across. the source of high voltage, and means are providedfor applying to the grid of the absorber either a positive or a negative potential as desired. It will thus be seen that with a suitable value of resistance and with the absorber ofsuitable current carrying capacity, when the grid of the absorber is made sufliciently positive the anode voltage of the intermediate amplifier will be reduced to a very small value, due to the voltage drop across the resistance, whereas, when the ab.- sorber' grid is made negative, the voltage drop acrossthe resistance or highly resistive impedance will only be that caused by the anode current of the intermediate amplifier, and consequently willnot appreciably aiiect the normal operation of that circuit. This follows from the ivell lmo\v11properties of the usualv'acuum tube. In this mannerby applying the said potentials to the absorber grid by a signaling key or switch, the anode potential of the intermediate amplifiercan be controlled, and in consequence the amplitude of the oscillations of the main amplifier will also be controlled;

According to the preferred embodiment of the invention shown in ,Fig. 1 of the draw ings, 1) represents an independent drive, source .of high frequency oscillations, generator of high frequency, energy, or oscillator circuit coupled to the grid circuit of an intermediate amplifier or electroirdischarge device V1, the plate circuit of which is coupled to the grid circuit ,ofthe final amplifier or. electron discharge device V2. A is an aerial which is energized by induction from the plate circuit of the amplifier, V2. G is a generator supplying the plate potentials of the amplifiers V1 andV2, the latter directly, and the former through a resistanceRL; i

Connected across the resistance or an impedance of high resistance R1 and the generator G is an absorber comprising tube V3, batteries B1 and B2, resistance R2 and modulating means in the form of switch K, which may conveniently be the usual type of telegraph key, arranged and connected as shown so that operation of the said switch K will apply modulating potentials to the rid, or in other words, will change the potential of the grid of the tube V3 from positive to negative, or vice versa, as will be more fully explained below.

It will be apparent that when the grid of vacuum tube V3 is positive, there will be a considerable drop of potential across the resistance R1, due to the current taken by the absorber circuit, and the potential applied to the plate or electrode of electron discharge device V1 other than the usual grid and cathode thereof; or in other words, an electrode of electron discharge'device V1 maintained at a higher potential than the usual grid and cathode thereof will therefore be considerably reduced. The switch K, therefore, serves to control the output from the tube V1 and the amplitude of the oscillations of the main amplifier V2.

B3 is a battery connected in the grid lead of the main amplifier V2, so as to apply a desired degree of negative bias in V2. This fixed negative bias is so chosen that when the absorber is rendered conductive and the oscillations of the intermediate amplifier are thereby reduced to zero, the anode current of the main tube will cease, that is, the tube is normally biased to cut off, as is usual in operating power amplifiers.

It will be seen,therefore, that by suitably proportioning the resistance'and absorber any required fraction of the full direct current load may be taken from the high voltage source and used up in the resistance during the time the absorber grid is positive, at which time the main amplifier takes no direct current, thus preventing voltage surges and variations in the direct current supply circuits when signaling.

In the description of the operation of this device, We will first consider the case when the switch K is closed. Under these conditions the battery B1 impresses a negative potential upon the grid of the tube V3, thereby reducing the flow of current through the resistance R1. This results in a small potential drop from the generator G to the plate of the tube V1, Which'therefore receives approximately its normal potential, films enabling it to operate as an amplier. I

In the event, however, that it is desired to reduce the degree of amplification, the switch is opened at K and due to the battery B2, thegrid is positively charged and there is a considerable flow of current through the resistance R1, which in turn causes a substantial potential drop across this resistance and consequently a lower plate voltage in the tube V1. As a result of this condition, the action of the tube Vl as an amplifier is materially reduced and, in fact, may be reduced to zero.

According to the construction shown in Fig. 2 the absorber and its associated grid bias control means are replaced by a switch S of the necessary current carrying capacity. When the switch S is closed, the potential applied to the plate of the tube V1 is reduced in a manner made clear in connection with the description of Fig. 1 above,-

owing to the resulting drop of potential across the resistance R1.

VVhile'we have shown and described the use of a single vacuum tube electron discharge device or triode for each oi the intermediate 1 and main amplifiers and also for the absorber, it will be understood that a bank of triodes or tubes may be used for this purpose, as is readily apparent to one skilled in the art.

Having thus described our invention, we claim and desire to secure by Letters Patent of the United States, the following 1. In a signalling system, an oscillator, an amplifier having input and output circuits the input circuit of which is coupled to said oscillator, a second amplifier coupled. to the output circuit of said first amplifier, said second amplifier having an output circuit, a single direct current source supplying direct current to both amplifiers, an impedance between the source and the first amplifier only and a modulating device connected across said source and impedance.

2. In a signalling system, an amplifier having input and output electrodes, means for impressing oscillations on the input electrodes, a circuit connecting the output electrodes and including a resistance and a current source serially connected, a variable impedance connected acrosssaid source and said resistance, and telegraphic keying means for rendering said impedance either high or low, whereby when said impedance is low the voltage drop in said resistance is high and the voltage across said output electrodes is substantially reduced.

3. In a signalling system, an amplifier having input and output electrodes, means for impressing oscillations on the input electrodes, a circuit connecting the output electrodes and including a resistance and a current source serially connected, an electron discharge device having its output circuit connected across said source and said resistance, a source of relatively positive potential, a source of relatively negative potential, and keying means for connecting either of said sources to a control electrode of the electron discharge device in order to lie lit;

vary the flow of current through the resistance and thereby vary the potential applied to the amplifier.

4. A transmitter comprising a master oscillator, first and Second electron emission tube amplifiers, a common source of direct anode potential for both of said amplifiers, a fixed impedance connected between the source and the tube anodeof one of said amplifiers and a modulating circuit of variable impedance connected in shunt with the source and fixed impedance for varying the anode potential applied to one of the amplifiers and means for simultaneously and appropriately varying the anode current supplied to the other amplifier.

'5. A transmitter comprising a master oscillator, an intermediate electron emission tube amplifier stage, apower amplifier stage, a common source of direct anode potential for both of said amplifier stages, a fixed impedance connected between the source and the tube anode of the intermediate amplifier stage, a modulator tube having its anode circuit in shunt with the source and fixed impedance, and modulating means for vary ing the potential of the control electrode of the modulator tube in order to vary the anode potential applied to the intermediate amplifier stage and means to simultaneously and appropriately vary the anode current supplied to the power amplifier stage.

6. A transmitter comprising a master oscillator, an intermediate electron emission tube amplifier stage, a power amplifier stage, means to negatively bias the power amplifier stage to cutoff, a common source of direct anode potential for both oi said amplifier stages, a fixed impedanceconnected between the source and the tube anode of the intermediate amplifier stage, a modulator tube having its anode circuit connected in shunt with the source and fixed impedance, a source of relatively positive potential, a source of relatively negative potential, and a key for impressing either the-positive or negative potential on the control electrode of the modulator tube according as the'key isopen or closed means controlled thereby for "decreasing the anode potential of the intermediate amplifier during key' open periods, and at the same'time to absorb the direct anode'cu-rrent which normally flows through'the power amplifier stage during the key closed periods;

7, In apparatus for electrical-currents, an electron discharge device having an electron emitting cathode, a "grid, and another electrode, a-resistanceconnected atone end to said electrode and at another point to a potential terminal, an impedance coupled to said resistance, and means for varying the value of said impedance whereby the current flowing through said potential'terminal and resistance is varied thereby varying by virtue said amplifier comprising an evacuated conof the potential fall across said resistance, the potential on the electrode to which said resistance is connected.

I 8. In apparatus for electrical currents, an

electron discharge device having an electron trode of said first mentioned electron discharge device is varied.

9. In a signaling system wherein high frequency undulatory energy is varied in accordance with relatively low frequency signalin g energy, an electron discharge device having within an hermetically sealed envelope an electron emitting cathode, a grid, and another electrode maintained at a relatively higher potential than said grid and cathode;

a resistance connected at one point to said electrode and at another point to a source of substantially unidirectional potential, an impedance associated with said resistance, a source of relatively high frequency energy coupled to said electron discharge device; and means for varying the value of said impedance in predetermined fashion whereby the current flowing through said resistance from said source'of substantially unidirectional potential is varied, thereby varying by virtue of the fall of potential acrosssaid resistance, the potential on the electrode to which said resistance is connected.

7 10. In a signaling system wherein high frequency undulatory energy is varied in accordance with relatively low frequency signaling energy, an electron discharge device having within an hermetically sealed envelope an electron emitting cathode, a grid and another electrode maintained at a resistance whereby the potential on said elecrelatively higher potential than said grid and cathode; a resistance connected at one point to said electrode and at another point to a source of substantially unidirectional;

potential across said resistance, the; potential on the electrode to which said resistance is connected; an amplifier associated'with said electron discharge device for amplifying modulated high frequency energytherefrom,

tainer having therein an electron emitting cathode, a control electrode, and another elec trode maintained ata potential relatively higher than the other electrodes of said amplifier; and, a connection from said source of substantially unidirectional potential to an electrode of said amplifier for suitably polarizing said last mentioned electrode.

11. In a signaling system utilizing propagated electromagnetic wave energy derived from the flow of modulated high frequency currents, the combination of an electron discharge device having an hermetically sealed container wherein are contained an electron emitting cathode, a grid, and another electrode maintained at a substantially unidirectional potential higher than said grid and cathode; a resistance connected at one point to said electrode and at another point to a source of substantially unidirectional potential, an impedance comprising an electron discharge device associated'with said source of potential and resistance; and, means for varying in predetermined fashion the current flow through said last mentioned electron discharge device and thereby the current flowing through said resistance whereby the potential on said electrode of said first mentioned electron discharge device is varied.

12. In a signaling system utilizing propagated electromagnetic wave energy de rived from the flow of modulated high frequency currents, the combination of an electron discharge device having an hermetically sealed container wherein are contained an electron emitting cathode, a grid,-and another electrode maintained at a substantially unidirectional potential higher than said gridand cathode; a resistance connected at one point to said electrode and at another point to a source of substantially unidirectional potential, an impedance comprising an electron discharge device associated with said source of potential and resistance; means for varying in predetermined fashion the current flow through said last mentioned electron discharge device and thereby the current 'fiowing through said resistance whereby the potential on said electrode of said first mentioned electron discharge device is varied; a source of high frequency oscillatory electrical energy coupled to the input side of said first mentioned electron discharge device; an amplifier comprising an evacuated container having therein a cathode a grid, and another electrode, coupled to the output side of said first mentioned electron discharge device in order to amplify the output thereof; a connection from said source of unidirectional potential to one of the electrodes of said amplifier for polarizing the electrode to which the source is connected; and, means for polarizing another electrode of said amplifier such that in the absence of currents to beamplified from said first mentioned electron discharge clevice, the unidirectional current flow through said amplifier is reduced.

13. In a communication system wherein electromagnetic.wave energy is propagated through space by virtue of the flow of sig nal modulated high frequency undulatory electrical energy, a source of high frequency electrical oscillations; an electron discharge device having input and output circuits, the input circuit of which is coupled to said source; an electron discharge device amplifier coupled to the output circuit of said first mentioned electron discharge device, said amplifier having an output circuit, a source of substantially unidirectional potential supplying potential to an electrode of said first mentioned electron discharge device; a resistance between said source and electrode; modulating means connected across said source and said resistance whereby the potential on said electrode is varied upon actuation of said modulating means; and a connection from said source to an electrode of said amplifier for polarizing the electrode so connected.

14. In a communication system wherein electromagnetic wave energy is propagated through space by virtue of the flow of signal modulated undulatory electrical currents, an amplifier having input electrodes and another electrode; means for impressing high frequency undulatory electrical energy on the input electrodes, a circuit connecting said other electrode of said device and one of the input electrodes thereof comprising a resistance and a unidirectional current source serially connected; and, modulating means associated with said resistance for varying the current flow therein and thereby the potential applied to said other electrode to which said resistance is connected.

15. In a communication system utilizing propagated electromagnetic wave energy derived from the flow of signal modulated high frequency undulatory electrical currents, an electron discharge device comprising an evacuated container having therein input electrodes and another electrode maintained ata higher positive potential than any one of said input electrodes, means for subjecting said input electrodes to high frequency electrical oscillations, a circuit connecting said electrode maintained at a higher positive potential and one of said input electrodes including a resistance and a current source serially connected, another electron discharge device having its output circuit associated with said source and said resistance, a source of modulating potentials, and means for. varying the current flow through said resistance in accordance with said modulating potentials whereby the flow of current through the resistance is varied thereby varying the potential applied to said electrode maintained at a relatively high positive potential.

16. In a communication system utilizing propagated electromagnetic wave energy derived from the, flow of signal modulated high frequency undulatory electrical currents, an electron discharge device comprising an hermetically sealed container wherein are contained a cathode, and a plurality of cold electrodes; an output circuit for said device; an input circuit for said device, means for subjecting a pair of electrodes of said devices to high frequency undulatory electrical potentials, and means for modulating the electrical potentials to which said electrodes are subjected comprising a source of substantially unidirectional electrical potential, a resistance in series therewith and in series with an electrode of said electron discharge device; and means for varying the current flow through said resistance in predetermined fashion, whereby the potential on the electrode to which said resistance is connected is varied in accordance with the predetermined variations in current flow through said resistance.

17. In a communication system utilizing propagated electromagnetic wave energy derived from the flow of signal modulated high frequency undulatory electrical 7 currents, an electron discharge device comprising an hermetically sealed container having therein a cathode and a plurality of cold electrodes; a circuit connected across said cathode and one of said cold electrodes, a circuit connected across said cathode and another cold electrode, said cathode and one of said cold electrodes being subjected to high frequency potentials whereby high frequency energy appears in one of said clrcuits; and, means for producing modulation in the high frequency energy appearing in one of said circuits, comprising a resistance and a source of substantially unidirectional potential connected in series with one of said cold electrodes and an electron discharge device associated with said resistance and source to produce in predetermined fashion changes in current flow through said resistance whereby the potential on said electrode connected in series with said resistance and source of potential is varied thereby producing modulation in high frequency currents appearing in said circuit.

18. In a communication system utilizing propagated electromagnetic wave energy derived from the flow of signal modulated high frequency undulatory electrical currents, a transmitting arrangement comprising a source of high frequency currents, first and second electron discharge devices coupled thereto, a common source of direct potential for an electrode in each of said electron discharge devices, a fixed impedance connected between the source and an electrode of oneof said devices and a modulating-circuit of variable impedance associated with the source and fixed impedance for varying the potential applied to the electrode of one of said devices connected with said source and impedance.

q 19 In a communication system utilizing propagated electromagnetic wave energy derived from the flow of signat modulated high frequency undulatory electrical cur rents, a transmitting arrangement comprising a source of high frequency currents, first and second I coupled thereto, a common source of direct anode potential for both of said devices, an impedance connected between the source and the anode of one of said devices, a modulating circuit of variable impedance connected in shunt with the source and said impedance for varying the anode potential applied to, one of the devices; and means for polariz ing the other of said devices whereby in the absence of high frequency currents in the output circuit of said one of said devices, the unidirectional current fiow through said other device is reduced.

20. In a system utilizing propagated electro-magnetic Waves derived from the How of signal modulated high frequency undulatory electrical currents, a source of high frequency potential, first and second electron emission tube amplifiers, a common source of direct anode potential for both of said amplifiers, animpedance connected between the source and the tube anode of one of said amplifiers, and, a modulating circuit of variable impedance connected in shunt with the source and impedance for varying the potential applied to one of said. amplifiers.

21. In a system utilizing propagated electro-magnetic waves derived from the {low of signal modulated high frequency undulatory electrical currents, a transmitting arrangement comprising a source of high frequency potentials, first and second electron discharge device amplifiers, a common source of positive potential for an electrode in each of said amplifiers, a resistance connect-ed be twcenthe source and an electrode-of one of said amplifiers, and, a modulating circuit of variable impedance connected across the source and resistancefor varying the potential applied to the electrode to which said resistance is connected.

22. In a system utilizing propagated electromagnetic waves derived from the flow electron discharge devices of signal modulatedhigh frequency undulastage following the intermediate stage, means to negatively bias the stage following the intermediate stage substantially to cut off, a common source of direct anode poten tial for both of said stages, an impedance connected between the source and the tube anode of the intermediate stage, a-modulator tube having its anode circuit connected to said source and impedance, a source of moduemitting cathodeand a plurality of cold electrodes, a resistance and a source of potential connected in series between said electron emitting cathode and one of said cold electrodes, means for causing currents to flow through said resistance in accordance with intelligence to be transmit-ted, another electron discharge device having an evacuated container wherein are contained an electron emitting cathode and a plurality of cold electrodes, an output circuit connected to output electrodes of said second mentioned electron discharge device, means for subjecting input electrodes of said second mentioned electron discharge device to high fre- 1 quency potentials, whereby high frequency energy appears in said output circuit, and, a connection from said resistance to a cold electrode of said second mentioned electron discharge device for varying the flow of high frequencyenergy in said output circuitin accordance with the current flow through said resistance.

24. In a system for transmitting intelligence, a master oscillator for generating high frequency oscillations, an amplifier coupled to said oscillator for amplifying the oscillations generated thereby, said amplifier comprising an hermetically sealed container wherein are contained an electron emitting cathode and a plurality of cold electrodes, an output circuit coupled to output electrodes of said amplifier; a vacuum tube having within an evacuated container an anode, a cathode and a grid, a resistance and a source of potential serially connected between said anode and cathode, means coupled to the grid and cathode of said vacuum tube for varying the current flow through said resistance, and, a connection from said resistance to one of the cold electrodes of said amplifier, for varying the high frequency oscillatory energy appearing in the output circuit of said amplifier.

NORMAN EUSTAGE DAVIS. WILLIAM THEODORE DITOHAM. 

